I've been monitoring performance of my solar panels for last two months and on two occasions my panels produced more power than they are rated. I have two Schott Poly 230W (made in USA) panels. On typical sunny day here in PNW they produce around 370-380 W around noon this time of year. But, on two occasions I got peek of 520 W, for short period of time, than they stayed around 480-495W for extended period of time, slowly coming down as they warm up. On first occasion I thought it was something wrong with my OutBack FM60, as it started acting up around that time. Controller eventually failed completely and I replaced it with TriStar MPPT60. Everything went back to normal, except last week the same thing happened: it was rather cold morning (52 F?), cloudy, with thick marine layer, when around noon sun broke through openings in marine layer, allowing full sun at cold panels. I again saw over 500W coming out of these panels, staying above 460W for next couple of hours. I think clear skies with low humidity helped as well. This time I have no reason to believe that controller had a problem. I know for sure that cold panels produce more power. Mine are rated at -0.44% per deg C, but that helps only partially. Anybody else observed something similar? Opinions? Would it make sense to cool solar panels somehow? Do you know of any working, effective cooling?

In warmer climes it's recommended to elevate the panels a bit if you are installing them flat on a solid surface. Just enough to allow air flow beneath them. Don't know how much it helps, but that's what I've been told.

I've wondered about this myself. There are couple of videos on youtube where water is run over an array. The rise in power was higher than I thought it would be. Had me wondering if it was worth while rigging up a flood system on a boat.

In the end, I didn't think it would be worth it as you would need to use fresh water (salt buildup would reduce output). You would use more energy making the fresh water then the gains.

Keeping your panels cool will definitely help in output power but you will use that same extra power pumping water, and water on the front of the panel may actually reduce power production if the water is at all murky.

Now what you saw has nothing to do with the temp of the panel, the is a thing call cloud edge effect, in some cases as the sun comes out from behind a cloud the edge of the cloud and the water droplets in it tend to concentrate the sun slightly. This effect will only last a few seconds to a few mins based on how fast the clouds are moving and are sometimes followed by a short period (Seconds to mins) of lower output.

Cloud edge effect is a factor, a big factor. But panels will produce higher than rated voltages when it is cold. If possible keeping some air space beneath the panels is a good idea, both for the panels operation and for providing shade underneath. Underneath is usually the Bimini or the cabin where people are. Trying to cool the panels is probably not worth it, but hosing dirt and dust off from time to time is.

Edited..is a response to #4......Hmmmmm... maybe... I wouldn't expect an instant power spike when the sun comes or goes in so maybe that is cloud edge effect... I found a bit about that effect which was something I hadn't heard of before.... however it would appear that cold is good regardless.
'The edge-of-cloud effect is only going to be a problem when it is very cold outside and passing clouds. You can use this sizing tool for SMA Sunny Boy Products. Also, solar panels have a Voc (open circuit) and a Vmp (max power). for a 12VDC panel Vmp may actually be 17VDC and Voc around 21VDC. Since the edge-of-cloud effect normally occurs when the inverter or controller is running you already have some extra wiggle room.

(I guess you could have a rolling black during the day and have your grid-tie inverter shut-off. But then you would also have to have record cold temperatures. But then it would be winter and you would have less transmitted light because it has to travel though more atmosphere at an oblique angle. Plus you would have to have perfectly clean panels. As you can see, not likely to happen any time soon.)'

The higher voltage when it is cold is only a problem when the input to the charge controller is close to being maxed out. Acquaintances in Alaska and Northern Canada have learned to leave extra head room on the charge controllers max voltage input rating since the panels will exceed their rated output when cold.

As FSMike says, don't mount them totally flat, leave a ventilation gap as this improves cooling significantly. I am not aware of anything else that is worthy of doing - just keep them clean. We clean ours every morning with a soft cloth with fresh water (we also run our 12v water maker daily) - one of the routines you get adopt - my job after putting the kettle on!

The first thing to be careful of is that the displays on the charge controllers can sometimes be quite optimistic, but panels can and do put out more than their rated power on occasions. There are several reasons for this:

1. Illumination level:

The panels are measured at 1000w/m2. While this is very bright, it is not exceptionally bright. In some situations particularly with direct sun and reflected sun from cloud the illumination levels can be higher, especially briefly.

2. Rating /Age:

Solar panels do age slightly, particularly when very new. The better manufacturers offer a guarantee regarding future output. Often when brand new they will exceed the rating slightly.
The better manufacturers also provide some idea of variance: 0 to +5%, -5 to +10% or -5 to+5%. For the first couple of examples, on average you should get a panel that exceeds the nominal wattage.

3. Temperature:

The panels are rated for a cell temperature of 25°C. In full sun they will generally be much hotter than this, but in cold climates especially when the sun briefly pokes out the temperature can be below 25°C and the output will be higher.

Your higher panel output will be a combination of these factors, but I think it likely your meter is over reading. They generally do.

Cooling the panels by leaving an air gap is important. If you can come up with a better method of cooling the panels (pumping seawater for example) this has potential to be useful. Invent away . I suspect the complication and required pump power means that it not really viable. There have been some suggestions of heating hot water for showering etc that could be combined with cooling the panels. I think this is promising. Cell temperatures are often around 45°C in summer conditions. This is warm enough to generate shower water, but pumping shower water temperature water around the panels would not cool them much.

I'm kinda surprised you guys are not thinking outside the box. Why not liquid cool the solar panels, and use that heat for one of your hot water sources?Solar Energy Advantages - DX3 Here is a crude example.
You might be able to custom fit some thermal collectors behind the solar using this technology:Build your own flat panel solar thermal collector
Then you would have both cool panels and hot water.
Just an idea....

One thing that you may have to consider when calculating your output is this; if your panels are putting out 500w for a few hours then your batteries are getting charged quite well. The more your batteries become charged, the less they need and your controller will change from bulk charge to ABS or float charging which will be at a much less rate that the bulk charge. You will only get a true maximum output reading if you batteries are somewhat depleted.

I use a little trick I developed in 1979. Freon, and fun with thermodynamics, called a co-generator.

Lloyd

Quote:

Originally Posted by BambooSailor

I've been monitoring performance of my solar panels for last two months and on two occasions my panels produced more power than they are rated. I have two Schott Poly 230W (made in USA) panels. On typical sunny day here in PNW they produce around 370-380 W around noon this time of year. But, on two occasions I got peek of 520 W, for short period of time, than they stayed around 480-495W for extended period of time, slowly coming down as they warm up. On first occasion I thought it was something wrong with my OutBack FM60, as it started acting up around that time. Controller eventually failed completely and I replaced it with TriStar MPPT60. Everything went back to normal, except last week the same thing happened: it was rather cold morning (52 F?), cloudy, with thick marine layer, when around noon sun broke through openings in marine layer, allowing full sun at cold panels. I again saw over 500W coming out of these panels, staying above 460W for next couple of hours. I think clear skies with low humidity helped as well. This time I have no reason to believe that controller had a problem. I know for sure that cold panels produce more power. Mine are rated at -0.44% per deg C, but that helps only partially. Anybody else observed something similar? Opinions? Would it make sense to cool solar panels somehow? Do you know of any working, effective cooling?